Expiration dating for Standard and Reference preparations has often been assigned arbitrarily; since references and standards are a critical part of release and research activities of the Center, the characterization of these materials with respect to chemical and immunological stability has begun. Using methods of SDS PAGE, 2-D, and crossed immuno-electrophoresis, Isoelectric Focusing and complementary immunoblotting techniques, Diphtheria and Tetanus toxin and toxoid preparations stored at different temperatures are being evaluated qualitatively. Work is in progress to obtain quantitative information in the development of inhibition ELISA methods. An additional feature of these studies involves the concurrent evaluation of the stability of anti-toxin preparations. Preliminary qualitative analyses indicate that immunological properties are retained for longer periods than originally anticipated; collection of data is continuing.